Alongside of its beneficial effects (support to vitamin D and melatonin production, antidepressant, well-being, etc), sun also causes short- and long-term misdeeds on skin: erythema, tissue premature aging, photodermatoses, carcinoma, melanoma (Ichihashi M. et al., Toxicology, 2003, vol. 189, pp. 21-39). And among the various families of rays that reach the earth's surface, ultraviolet rays limited to ultraviolet-A (λ 320-400 nm, UV-A) or ultraviolet-B (λ 290-320 nm, UV-B) radiations have been identified as being the source of such misdeeds.
Skin has however intrinsic defense systems that enable it to fight against sun damages. Thus as a result of sun radiation, a so-called natural or internal photoprotection already expresses therein, which is ensured by a production of photoprotective melanin pigments, or else by a thickening of stratum corneum with a greater number of keratinocyte layers in epidermis. Trans-urocanic acid which is a histidine metabolite and is present in high concentration in the upper layers of epidermis and particularly in stratum corneum, is also involved in this natural photoprotection by expressing an endogenous protective role against the harmful action of UV-B (Barresi C. et al., J. Invest. Dermatol. 2011, vol. 131, pp. 188-194).
Skin protection against sun radiation can also be induced extrinsically (Lacour et al., Annales de Dermatologie et Vénéreologie, 2007, vol. 134, pp. 18-24). In general, such a photoprotection, that can be qualified as artificial compared to natural photoprotection, is ensured by external means comprising the topical application of photoprotective cosmetic products, in addition to covering clothing. These products or preparations usually contain protective substances dissolved or dispersed in an excipient and that can be classified into three broad categories: sunscreens whose action is to reflect all sun radiations and therefore to prevent their penetration into skin; filters whose action is to absorb a part of sun radiations, usually ultraviolet-A (320-400 nm) and B (290-320 nm) rays and then to release the photon energy absorbed by heat exchange with skin; and finally photoprotective agents which are said active compared to sunscreens and filters and which are usually substances capable of trapping reactive oxygen species (“ROS”) formed when radiations are absorbed by molecules naturally present in skin (photo-sensitization mechanism).
Such topical preparations are generally characterized by a sun protection factor (“SPF”), which is an indicator of the protection level against erythema (sunburn) and which is adapted to sunlight conditions and to peculiar skin phototypes. For sun protection formulations with high SPF, sunscreens and filters are associated.
Sunscreens in such preparations are mostly inert substances of mineral origin (powders: zinc oxide, titanium dioxide, etc). Their use in sunscreen formulations remains however cumbersome with the appearance of white marks when they are applied. A presentation under the form of nanoparticles improves the marketing of these sunscreens, although their safety in this form has been challenged for a few years with a potential risk to penetrate skin.
Organic chemical filters are generally of synthetic origin, or of natural origin when they are oils or extracts derived from plants. Their efficiency consists of an absorbing effect of ultraviolet light due to the structural presence of chromophore groups capable of absorbing, then dissipating light rays with specific wavelength. The chromophore groups in these chemical filters are almost systematically compounds bearing a mono- or polycyclic aromatic ring (phenyl, benzyl, benzylidene, benzoyl, naphthyl, anthracenyl, etc) which is conjugated to carbonyl groups or aliphatic unsaturated systems for a greater delocalization of electrons under the effect of absorbed radiations (excited state), before returning to a stable state with dissipation of the received photon energy and/or re-emission of a less dangerous radiation (for example infrared).
Thus, there may be mentioned among these chromophore chemical filters which belong to the state of the art (R. Rai and al., Indian J. Dermatol., 2012, vol. 57(5), pp. 335-342) and are commercially available, the following compounds whose absorption spectrum is rather UV-B-specific:                para-aminobenzoic acid (PABA) ester derivatives, such as 2-ethylhexyl-4-dimethylaminobenzoate (padimate O),        methoxycinnamic acid derivatives such as octyl methoxycinnamate (octinoxate or OMC) and 2-ethoxyethyl-methoxycinnamate (cinoxate),        salicylic acid derivatives such as ethylhexylsalicylate (octisalate) and trolamine salicylate,        2-ethylhexyl-2-cyano-3,3-diphenyl-2-propenoate (octocrylene),        phenyl-benzimidazole sulfonic acid (ensulizole).        
There may also be mentioned the following compounds whose absorption spectrum is rather UV-A-specific:                dibenzoylmethane derivatives such as butyl methoxydibenzoylmethane (avobenzone),        terephtalidene dicamphor sulfonic acid (ecamsule or Mexoryl SX®).        
There may finally be mentioned the following compounds whose absorption spectrum is wider (UV-B and UV-A radiations):                benzophenones such as benzophenone-3 (oxybenzone) and benzophenone-8 (dioxybenzone),        hydroxybenzotriazoles derivatives,        new triazines such as benzoxazines (Bruge and al., PLoS ONE, 2014, 9, e83401.).        
For many of these organic filters that are primarily chosen for physico-chemical criteria (SPF, absorption spectrum, persistence to skin surface), it emerges beyond some potential allergic disorders (contact allergies, photo-allergies, itching) yet reported over the last few years (Uther W. and al., Contact Dermatitis, 2014, vol. 71, pp. 162-9), that the photochemical innocuousness of these chromophores agents, especially of their degradation products such as the photo-isomerization products, is not always indicated.
More recently, other protective strategies have been developed with the introduction of active agents in sun formulations, such as DNA repair enzymes and above all antioxidants like vitamins C and E, or polyphenols (MS Matsui and al., J. Invest. Dermatol., 2009, vol. 14, pp. 56-59). The interest in this strategy has been reinforced with recent evidence of the capacity of visible (400-700 nm) and near infrared (700-1440 nm) radiations to induce the formation of ROS in the skin (F Liebel and al, J. Invest Dermatol, 2012, vol 132, pp. 1901-1907; Schroeder P. and al., Exp Gerontol, 2008, vol 43, pp. 629-632). Once again, the inclusion of such active ingredients in topical formulations is not without raising troubles: lack of stability, cost, and above all the formation, when in contact with oxygen or its reactive species, of by-products whose toxicology is often unknown.
Accordingly with regard to these different facts, the applicant focused on identifying new photoprotective compounds for topical cosmetic purposes and with a broad-spectrum protection against sun radiation, along with a concomitant objective to design products that do not form degradation or photo-conversion by-products which could be poorly tolerated by skin. Ensuring evidence of the innocuousness of substances of interest, but also of the innocuousness of reaction by-products resulting from the targeted cosmetic activity, has become of high priority in the cosmetic or dermocosmetic industry.